What if a black hole formed near our solar system?

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It’s been weeks since the weirdness began in the night sky and, like everyone else, you’ve been glued to the news. Tonight, there’s coverage of the president’s speech, followed by more analysis by astrophysicists, geologists and climatologists. Like a bad joke, they speak in terms of "good news" and "bad news."

The good news is we’re not all dead, and the planet isn’t destroyed, hurtling off into space or swirling down the gravitational drain into the sun.

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The bad news is we’re in for some "pretty interesting climate shifts." As it turns out, surviving a near miss with a black hole is a bit like escaping the Titanic -- only to freeze to death in the North Atlantic.

Black holes rank among the most fearsome phenomena in the universe. Their gargantuan gravity warps space and time -- and our understanding of them -- almost to the breaking point. Looming larger still are the supermassive black holes skulking in galactic cores, the repositories of millions to billions of stars’ worth of matter [source: Lemonick].

What mayhem might one of these black beasts bring if it formed, or passed, near our solar system?

As with most hypothetical questions, the devil is in the details. How close would the black hole approach as it swung by? Where would it come from? How massive would it be?

First off, our sun will never become a black hole; it would need 10-15 times as much mass in order to undergo the kind of gravitational collapse required [source:GSFC]. Nor will any stars in our galactic neighborhood undergo the big crunch: Most nearby twinklers are red dwarfs -- mighty mites as common as Starbucks in Seattle -- and pack only a fraction (8-60 percent) of our sun’s mass [sources: Encyclopaedia Britannica, Filippenko].

That leaves two possibilities: Either a black hole spontaneously forms in our vicinity, or a rogue passes nearby. The protestations of Large Hadron Collider naysayers notwithstanding, we can discard the first possibility (we’ll explain why later).

As for the second possibility, astronomers and astrophysicists confirmed the existence of wandering black holes in 2000, but the chances of one hitting us are roughly nil [sources: 20/20; Unruh]. As novelist Douglas Adams once put it, "Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space."

That said, the possibility is far too interesting not to explore.

Black Hole Effects on Space and Time

From a distance, a black hole acts like any massive, gravitational object: Until it's right on top of you, it follows classical mechanics and Newton's law of universal gravitation, which tells us the attraction between two objects is proportional to their masses and drops off rapidly with distance. In other words, there's no gravitational difference between R136a1, a blue dwarf star weighing 265 suns, and a 265-solar-mass black hole [source: Fazekas].

Approach close enough for a black hole to wrap you in its gravitational sleeper hold, however, and you're grappling with a different set of rules: Einstein's general theory of relativity, which predicted black holes, says that gravity also warps space and time, and that extreme gravity does it, like Vanilla Ice, to the extreme.

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If you wanted to study a black hole from a starship, you'd find that, the closer you got to the monstrous mass, the more oomph your engines would have to kick out to maintain a circular orbit. At first, firing off the occasional rocket burst would suffice to stabilize you; closer in, and you'd have to expend enormous energy just to maintain an irregular orbit. Closer still, and nonstop rocket burn would be all that stood between you and annihilation.

Once you ran out of fuel (or succumbed to space madness and turned off the engines), you would spiral in to the black hole's event horizon, a boundary beyond which nothing, not even light, can escape. From there, you'd have a date with destiny: Nothing you could do would stop your inexorable journey toward the singularity, a core of infinitely distorted space-time where physics as we know it curls up in a ball and whimpers.

All through your approach, time would have slowed -- a lot. From your point of view, nothing would have changed but, to a friend watching from far away, time around you would flow less like greased lightning and more like sap on a cold February morning. Just outside the event horizon, you would appear to stop. Since light cannot escape the event horizon, that would be the last your friend would see of you.

Gravitational time warps occur universally but are usually too feeble to be noticed. On Earth, for example, you would age one-billionth of a second less each year at sea level than you would atop Mount Everest [source: Harvard-Smithsonian].

Within a black hole, time twists even more. In fact, when we say you can't avoid falling into the singularity, it isn't just because of the intense gravity or space warping: Rather, time within a black hole warps to such a degree that the singularity literally lies in your future. Trying to prevent reaching the singularity would be like attempting to halt time.

Read on to see what would happen if our solar system chanced upon such a flume of force.

Tripping the Light Fantastic

Gravity prevents light from escaping a black hole in the Einsteinian sense, not the Newtonian: The force can't "pull" on light, because light has no mass. Rather, gravity warps space-time back on itself to such a degree that light resembles a hamster in a wheel, running for all it's worth but getting nowhere [source: Royal Greenwich Observatory].

Picture a black hole as a waterfall of space, where space pours past photons just as quickly as they "swim" through it -- that is, at light speed [source: Hamilton].

The Day of Doom

Suppose a far-off black hole is locked in a binary embrace with a star that goes supernova. Suddenly freed, the gravitational giant shoots our way at tens to hundreds of kilometers per second. How would we know?

The short answer is, we wouldn't -- at least, not until it interacted with something -- because a black hole's massive gravitation denies escape even to light. So, instead of trying to spot a peppercorn on a black carpet, let's look at a few ways we might identify a black hole indirectly.

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First, matter ripped apart by a black hole emits radiation as it swirls into its accretion disk, causing the area around it to "shine" like a feather boa under klieg lights.

Second, the black hole's distortion of surrounding space, if spotted by earthlings, could also render it detectable. This gravitational lensing, predicted by Einstein's general theory of relativity, has been observed by astronomers near massive objects like galaxies, black holes and our sun [sources: STSI; University of Illinois].

Even under ideal circumstances, however, spotting a black hole this way would harder than finding a flea on a speckled dog at night -- with binoculars. And an eye patch. For gravitational lensing to be visible from Earth, the black hole must pass between us and a star; for us to spot it, it must transverse the star, so that astronomers have a normal view to compare it to. Even if this were to happen, which is unlikely, the size of both the black hole and of the lensing effect would be so miniscule that we'd be lucky to spot it even if we were looking for it [source: Unruh].

Finally, a black hole could make itself known by interacting gravitationally with celestial objects like planets, stars, asteroids or comets, which brings us to a key question: How close does our hypothetical black hole pass by our solar system?

Clearly, the closer it passes, the worse the damage. A near miss could severely perturb planetary and lunar orbits, like a sparrow slamming into a spiral spiderweb, dragging the curved orbits into a tangle of interactions.

From our perspective on Earth, the tides would change and the sky would alter. If the black hole's gravity kicked our orbit farther from the sun or closer inward, or made it more elliptical, we would suffer shifts in global temperatures and seasons, or possibly worse. In the worst case (short of becoming a black hole amuse-bouche), Earth might be thrown into the sun, or sent hurtling out into space on an escape trajectory, doomed to freeze and die.

As well-known astrophysicist Neil deGrasse Tyson once told news program "20/20" with characteristic understatement, "It would be a bad day for the solar system if we got visited by a black hole."

With that in mind, let's stop dancing around the event horizon and dive right in.

Hawking Radiation

Everywhere, all the time, pairs of positive and negative "virtual particles" pop briefly into existence, then recombine and annihilate one another. What would happen to such particle pairs at a black hole's event horizon? According to physicist Stephen Hawking's theory, the negatively charged particles would be caught by the black hole, whereas the positively charged ones would escape. This Hawking radiation, if it weren't too faint to detect, would provide another way to spot black holes in space [source: Economist].

First Contact: The Good News and the Bad

Bruce, you may be a diehard, but even you can't save us from this Armageddon scenario.

Doomed -- there's no other word for it. The scientists have crunched the numbers, and we're in the black hole's path. Even Bruce Willis and a plucky crew of nuke-toting oilers can't save us now.

The tug of the black hole's gravity on Neptune provides our first solid clue that something dire is afoot. Astronomers know Neptune's orbit so well that they can detect a deviation in it as small as 1 arc second (a unit of angular measure). A typical 10-solar-mass black hole moving at a characteristic speed of 300 kilometers per second (671,081 mph, or about one-thousandth the speed of light) would cause that much ruckus while still one-tenth of a light-year out [source: Hamilton].

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Here's our last bit of good news: A black hole of such a size moving at such a clip would give us around 100 years of warning in which to get our act together. A slower moving black hole might give us 10 times that long. Either way, it's time to start building that space ark, folks [source: Hamilton].

As it passes close by Neptune, the dark destroyer pulls the gas giant into its orbit. The planet looks strange now: As it moves away from us, its colors appear redshifted -- the wavelengths of its radiation, including light, stretch out, shifting toward the red end of the spectrum. As Neptune passes behind the black hole, gravitational lensing makes it appear to flatten and warp around the murky sphere. As the planet emerges again, heading toward us, its colors look blueshifted -- its emission wavelengths bunch up, shifting toward the blue end of the spectrum.

Redshifting and blueshifting usually result from a stellar object moving away from us or toward us, respectively, much like the Doppler shift of a siren as an ambulance passes us; around a black hole, they're also a consequence of the way extreme gravity warps time.

Soon, the black hole tears the gas giant apart, stripping its component gases off in a swirling gravity spiral, the accretion disk, like spun sugar in a cotton candy machine. From our perspective, it seems to take forever to spiral into the event horizon. Meanwhile, the light released by Neptune's death throes outlines the black hole in negative, like the sun's corona during a solar eclipse.

As the black hole closes on Earth, we can finally see its surrounding starfield bend and stretch from lensing, like something in a funhouse mirror. Every available telescope turns to watch this distortion and the black emptiness at its center.

If our dark destroyer is a supermassive black hole, the story is already over; its event horizon looms as much as five times as large as our solar system [source: Marder]. But what fun is that? Let's see what one of these monsters looks like on the inside.

The End of the World, or Through the Looking Glass

You climb into your indestructible pod, knowing it will spare you only briefly, but hoping at least to survive long enough to experience the black hole's interior. Launching into space, you plot a gentle, decaying orbit inward.

Luckily for you, but unluckily for the solar system, this is a supermassive black hole. Yes, we're changing the rules, but everything would happen far too quickly if we didn't. Here's why:

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In a small black hole -- say, around 30 solar masses -- the tidal forces caused by the steep intensification of gravity over distance would tear you apart long before you reached the event horizon. In fact, at the event horizon, the tidal force between your head and your feet would be around 1 million G's (Earth gravities). Even if you could survive, there would be no time to enjoy your victory, for you would encounter the singularity 0.0001 seconds after crossing the event horizon [source: Hamilton].

In a supermassive black hole sporting the mass of 5 million suns, like the one at the center of our galaxy, the experience is much different. Any black hole that bulks up to more than 30,000 solar masses exerts head-to-toe tidal forces of less than 1 G at its event horizon. There's also more time for sightseeing on the way to your doom: On a curved descent, it will take you 16 seconds (and change) to reach the singularity after crossing the event horizon (this "infall" time is a function of the black hole's mass; the more mass, the longer it takes) [source: Hamilton].

Falling through the event horizon of a black hole is a bit like falling asleep or falling in love: It's hard to pinpoint when it happens, but once it does, your sense of reality is significantly compromised. In the case of the black hole, you can still see the starfield (light can get into a black hole, it simply cannot leave), but the view reminds you of the whorls of color inside a soap bubble, and there is something else wrong, too: The curved space-time garbles and twists light, confusing your binocular vision; it's like peering through a kaleidoscope with your eyes crossed [source: Hamilton].

Tidal forces stretch your craft downward like taffy and crush inward on you from every side. As you near the singularity, you witness an extraordinary sight: The outside universe appears to compress into a bright, thin, blueshifted band around your waist, as the views above and below dim and redshift. After that, what's left of your shredded matter enters a point of infinite curvature, where known space and time end.

The Large Hadron Collider

Soon after the Large Hadron Collider (LHC) came online, the news and the Internet were abuzz with fears that an LHC-spawned black hole would destroy the Earth. Here's why you should buy those green bananas anyway: According to Einstein, the LHC cannot create microscopic black holes. Even if it could, as some have hypothesized, they would disintegrate instantly or, if not, would pass through the Earth into space. How do we know? Because if these microscopic black holes exist, then cosmic rays already make them when they collide with the Earth so, if they were dangerous, they would have already destroyed us [source: LHC].